1. Field of the Invention
The present invention relates to the field of reaction injection molding and more particularly to methods for introducing reactants into molds or combinations of components of articles to be connected together. This method can be employed advantageously with the implementation of high impingement mixing technology.
2. Description of the Prior Art
Reaction injection molding (RIM) deals with the metering of precise amounts of two or more reactants through a head. A piston in the RIM head pushes out the residues in the chamber leaving a clean chamber for another shot. The components are shot into a closed chamber or mold where they react, foam, set, and cure. In conventional low density foams in the thermal container industry, foams react in eight to ten seconds; set in 1.5 to 2.0 minutes; and cure in six to eight minutes. In prior art methods, an operator places a body member under the nozzle or head of a conventional foaming machine or moves the head to a body which is already situated in a cavity. If the body is not already in a cavity it is placed in one. A liner is then placed over the body and the fixture is closed. A conventional machine has a mixing chamber in which two streams of reactants are mixed prior to injection into the body. Following injection, any residue that remains in the mixing chamber of the foaming machine will react and foam. Such residue is usually expelled by pouring a flushing agent such as methylene chloride through the mixing chamber. During this flushing operation, various gases are released into the atmosphere, as well as those reacting on the unit body before the liner is placed on the body and fixture closed. Other problems with prior art methods include inconsistent size of reactant charges, relatively long delays while reactants set and cure, inconsistent ratio of material components, losses of foam in the residues, and poor cell structures and fills. In a typical injection process, a foam head is inserted into a mold containing components of an article, but often the head is not inserted properly and pushes the components together into undesired proximity and causes the resultant article to be deformed. Improper insertion of the head also results in the injection of an incorrect amount of foam.